Electroplated article



y 4, 1956 c. F. SMART 2,755,537

mmc'mormm ARTICLE Filed Aug. 22. 1952 'I/I/I/II/I/IIII/III/IIIIIIIIIIIIII/III/I/IIII/IIII[III/III,

Inventor Clare/2c? 2 31mm Attorneys ELECTROPLATED ARTICLE Clarence F. Smart, Birmingham, Mich, assignor to General Motors. Corporation, Detroit, Mich., a corporation of Delaware Application August 22, 1952, Serial No. 305,850

10 Claims. (Cl. 29.196.6)

This invention relates to composite metallic articles and in .particular to metallic articles having outer coatings of antimony or antimony alloys.

I have found that electroplated articles may be provided with a smooth, corrosion resistant adherent surface when the-outer electrodeposited coating is formed of antimony or an antimony alloy. An antimony or antimony alloy coating formed according to my invention produces a corrosion resistant coating on a base article. The coatings produced according to my invention also provide a surface which is an excellent undercoat for the electrodeposition of coatings of other metals. For example, in the production of chromium plated articles using a conventional hot, oxidizing, highly. corrosive chromium plating bath, an antimony or antimony alloy undercoat formed according to myinvention withstands the attack of the corrosive chromium plating bath and provides a surface on which chromium may be electrodeposited to form an adherent surface.

A principal object of my invention thus is to provide a composite metallic assembly having a surface of antimony or an antimony alloy, A further object is to provide a metallic structure including a plurality of smooth, adherent electrodeposited coatings having an outer coating of antimony or an antimony alloy. Other objects and advantages will more fully appear as the description proceeds.

In general, my invention comprises a composite electroplated metallic structure having a metallic base, a protective coating for the base and corrosion-resistant coatings of antimony or alloys of antimony. If desired, a metallic structure embodying my invention may serve as a base for further electrodeposits of chromium, nickel or other metals. Whiel the following description sets forth in detail'certain specific illustrative embodiments of my invention, these are indicative of but a few of the various ways in which the principle of my invention may be em ployed.

In thedrawing, illustrating diagrammatically one specific embodiment wherein chromium is plated over an article embodying my invention, 1 represents a base metal; 2 a coating of lead, indium, or an alloy of lead and indium; 3 a layer of an alloy containing lead and antimony; 4 a layer of antimony; and 5 a layer of chromium.

Referring more particularly to the embodiment of my invention as shown in the drawing, the base metal 1 preferably isany metal conventionally electroplated such as iron, steel, brass, copper or zinc, According to my invention, however, a composite structure may also be prepared on articlesformed of other base materials such aslead, tin, nickel, cadmium, indium or alloys of these metals.

In the drawing 2 represents a protective layer of a relatively inert metal. The use of such a coating is very desirable in a practical application of my invention because it protects the base metal 1 from corrosion or etching in conventional'acid plating baths used in plating subsequent layers. This layer 2 may be applied in an alkaline bath which does not readilyv attack or corrode the base, metal. The use of this protective coat is also 2,755,537 Patented July 24, 1956 desirable over abase. metal formed of copper, brassor other copper containing metals or over a base metal having a coating of; copper on its surface because there is otherwise a reaction between the copper containing metal and the later depositedantimony or antimony base alloys resulting, in a brittle interface structure which causes the deposited antimony containing layer to crack and peel. While the layer 2 maybe of any metal or alloy resistant to attack by the treatment to which it may be subjected, such as a lead-antimony alloy, I have obtained very beneficial resultswhen it.is a coating of lead, indium or an alloy of indium and'lead. The layer 2 may have any desired thickness. In a preferred embodiment of myinvention, this layer is afiash coating 0.00001 to 0.0001 inch thick.

The layer 3 may be of an alloy containing lead and antimony, either of which may be the major constituent. If desired, it also may be composed of two separate layers, one of a lead-antimony alloy (an alloy in which lead is the major constituentland the other of an antimonylead alloy (an alloy in which antimony is the major constituent). The purpose of the layer 3 is to build up the electrodeposit to any desired thickness and to form a base to which other layers will adhere. In addition, when used with a copper base material or another base material having a copper coating, it has the further advantage of preventing any discoloration of the outer surface by a bleeding through of copper. An alloyv containing lead and antimony is a preferred build up coat because it adheres firmly to its own undercoat metal and provides a surface to which an electrodeposited antimony layer will readily. and firmly adhere. If desired, however, other metals or alloys may also be used for this build up layer. This build up layer 3, of course, may be of any desired thickness. In a preferred embodiment it is a bright coating having a thickness of from 0.0005 to 0.0015 inch.

The layer 4, is of antimony, This antimony layer forms an adherent corrosion resistant outer coating for the article being plated. However, if it is desired to electrodeposit an additional coating of other metals such as nickel, chromium, etc., the antimony coating provides a surface resistant to the attack of corrosive plating baths, to which other metals or alloys may be electrodeposited to form an adherent outer coating. While this layer 4 also may be of any desired thickness, I have found that optimum results are obtained when it is from 0.0005 to 0.0015 inch thick.

While the thicknesses of the various individual metal layers deposited on the base member may be varied as desired, I have found that very beneficial results are obtained if the composite thickness of these layers when dc posited on a base metal of brass is from 0.0001 to 0.0005 inch and when deposited on a base metal formed of zinc or steel is from 0.0005 to 0.003 inch.

As illustrated in the drawing, in one specific embodiment of my invention a layer 5 of chromium may be plated on the composite structure. Its thickness, of course, may also be varied and will be dictated by the particular application intended. thin layer of chromium, such as a flash coating, is pre ferred In determining the thickness of the chromium layer, the problem is one of obtaining an abrasion-resistant layer with a minimum amount of chromium. l have found that a chromium flash coating having a maximum thickness of about 0.00001 inch deposited over an undercoat of antimony or antimony alloy produces a chromium surface 6 which is both lustrous and abrasionresistant. If desired, the chromium surface. 6 may be bufied or polished to increase its luster. the use of properplating baths and procedures, a smooth. bright chromium surface which requires. no polishing or butfing maybe obtained'in the plating process itself,

In general, a relativelyv However, by

While the specification has described an article having an outer coating of chromium, it will of course be understood that my invention is not to be limited solely to articles which are to be chromium plated. Metallic articles having the various intermediate coatings according to my invention may be plated with other metals as Well or, if desired, need not have any additional coatings.

In a variation of my invention, the layer 3 as shown in the drawing, of an alloy containing lead and antimony may be omitted and a single layer 4 of antimony used to both build up the thickness of the composite plate and to serve as an outer coating or as a base for any further coatings. If desired, in another variation, the antimony layer 4 may be omitted and the coating thickness built up With the layer 3 of an alloy containing lead and antimony.

In preparing a multilayer metal structure according to my invention, it is, of course, understood that the various intermediate metal layers may be applied in any suitable manner, for example, as by coating, spraying or rolling. However, in a preferred form, the various metal layers are plated from electroplating baths suitable for the particular metals being applied. Since the brightness of a deposited layer is dependent on the surface quality of its own undercoat, it is desirable in the application of each metal layer to obtain as smooth and bright a deposit as possible so that the necessity for any final buffing or polishing Will be eliminated.

The protective coating 2 may be deposited on the base metal form any suitable plating bath conventionally used in plating of these metals. An example of a satisfactory alkaline bath for the plating of a lead coating is one containing per liter of water, about 100 to 120 grams of Rochelle salts, to 25 grams of lead oxide, lead acetate, or lead carbonate, to 75 grams of tetra sodium salt of ethylene diamine tetra acetic acid. Sodium hydroxide may be added as needed to maintain the pH at about 9 to 11. Lead anodes may be used.

Any suitable bath may be used in the plating of a coating of indium or alloys of lead and indium. For example, the baths disclosed in my prior Patent No. 2,423,624 may be used.

In plating antimony or alloys containing antimony, plating baths such as those disclosed in my co-pending application Serial No. 291,563, filed June 3, 1952, may be used and the metals plated by electrodeposition from such baths. On the other hand these metals may also be plated from any conventional antimony plating baths.

An example of a bath suitable for the plating of chromium on a structure embodying my invention is one containing 53 ounces per gallon of chromic acid and 0.53 ounce per gallon of surfuric acid. The bath gives a lustrous deposit of chromium When used at about 120 F. Other baths such as those containing added brightener agents are also suitable. The antimony undercoating of my invention successfully resists the corrosive attack of these oxidizing baths and provides a surface to which the chromium will firmly adhere.

Various changes and modifications of the embodiments of my invention disclosed herein may be made by those skilled in the art without departing from the principles and spirit of the invention, as set forth in the appended claims.

I claim:

1. A metallic structure comprising a metal base, a first layer of a metal selected from the class consisting of lead, indium, and an alloy of lead and indium, a second layer of an alloy containing lead and antimony and a third layer of antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch, the thickness of the second layer being from 0.0005 to 0.0015 inch and the thickness of the third layer being from 0.0005 to 0.0015 inch.

2. A method of producing a composite metallic article comprising the steps of electrodepositing on a metal base member a first layer of a metal selected from the class consisting of lead, indium and an alloy of lead and indium, a second layer of an alloy of lead and antimony 4 and a third layer of antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch, the thickness of the second layer being from 0.0005 to 0.0015 inch and the thickness of the third layer being from 0.0005 to 0.0015 inch.

3, A metallic structure comprising a metallic base, a first layer of a metal selected from the class consisting of lead, indium and an alloy of lead and indium and a second layer of an alloy of lead and antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch, and the thickness of the second layer being from 0.0005 to 0.0015 inch.

4. A metallic structure comprising a metallic base having a first layer of a metal selected from the class consisting of lead, indium and an alloy of lead and indium, a second layer of a lead-antimony alloy and a third layer of an antimony-lead alloy, the thickness of the first layer being from 0.00001 to 0.0001 inch, the thickness of the second layer being from 0.0005 to 0.0015 inch and the thickness of the third layer being from 0.0005 to 0.0015 inch.

5. A composite metallic structure comprising a metal base, a first layer 0.00001 to 0.0001 inch thick of a metal selected from the class consisting of lead, indium and an alloy of lead and indium and a second layer 0.0005 to 0.0015 inch thick of a metal of the class consisting of antimony and alloys of antimony.

6. A metallic structure comprising a metal base, a first layer of a metal selected from the class consisting of lead indium and an alloy of lead and indium, a second layer of an alloy containing lead and antimony, a third layer of antimony and a fourth layer of chromium, the thickness of the first layer being from 0.00001 to 0.0001 inch, the thickness of the second layer being from 0.0005 to 0.0015 inch, the thickness of the third layer being from 0.0005 to 0.0015 inch and the thickness of the fourth layer not over 0.000001 inch.

7. An article of manufacture comprising a metallic base member having a first layer thereon of indium and a second layer of antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch and the thickness of the second layer being from 0.0005 to 0.002 inch.

8. An article of manufacture comprising a metallic base member having a first layer thereon of an alloy of lead and indium and a second layer of antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch and the second layer being from 0.0005 to 0.002 inch.

9. The method of producing a corrosion-resistant article comprising the steps of separately electrodepositing on a metal base member a first layer of indium and a second layer of antimony, the thickness of the first;

layer being from 0.00001 to 0.0001 inch and the thickness of the second layer being from 0.0005 to 0.002 inch.

10. The method of producing a corrosion-resistant metal article comprising the steps of separately electro-- depositing on a metal base member a first layer of an alloy of lead and indium and a second layer of antimony, the thickness of the first layer being from 0.00001 to 0.0001 inch and the thickness of the second layer being from 0.0005 to 0.002 inch.

References Cited in the file of this patent UNITED STATES PATENTS 1,168,663 Mark Ian. 18, 1916 1,314,603 Mott Sept. 2, 1919 1,341,938 Shoemaker June 1, 1920 1,378,439 Baskerville May 17, 1921 1,956,467 Palm; Apr. 24, 1934 2,039,069 Domm Apr. 28, 1936 2,120,738 Domm June 14, 1938 2,176,066 Carleton Oct. 17, 1939 2,388,019 Strickland Oct. 30, 1945 2,567,934 Green Sept. 18, 1951 2,634,235 Hitchens Apr. 7, 1953 2,658,266 Du Rose Nov. 10, 1953 

1. A METALLIC STRUCTURE COMPRISING A METAL BASE, A FIRST LAYER OF A METAL SELECTED FROM THE CLASS CONSISTING OF LEAD, INDIUM, AND AN ALLOY OF LEAD AND INDIUM, A SECOND LAYER OF AN ALLOY CONTAINING LEAD AND ANTIMONY AND A THIRD LAYER OF ANTIMONY, THE THICKNESS OF THE FIRST LAYER BEING FROM 0.00001 TO 0.0015 INCH, THE THICKNESS OF THE SECOND LAYER BEING FROM 0.00005 TO 0.0015 INCH AND THE THICKNESS OF THE THIRD LAYER BEING FORM 0.0005 TO 0.0015 INCH. 